This application is based on and claims priority to Japanese Patent Application No. 2001-132469, filed Apr. 27, 2001, the entire contents of which is hereby expressly incorporated by reference.
1. Field of the Invention
The present invention relates generally to a rocker arm arrangement for an engine, and more particularly to an improved rocker arm arrangement for an engine in which a biasing member urges a rocker arm toward a stopper.
2. Description of Related Art
A four-cycle engine is one of the most popular engine types used in, for example, an outboard motor. The four-cycle engine typically includes intake and exhaust valves to selectively connect a combustion chamber with an air intake system and an exhaust system, respectively. Typically, one or more camshafts directly or indirectly actuate the intake and exhaust valves. An engine, for example, having a camshaft that indirectly actuates the intake and exhaust valves can employ rocker arms that operate between the camshaft and the intake and exhaust valves. The rocker arms are mounted on a rocker arm shaft that extends generally parallel to the camshaft.
The rocker arms pivot about the rocker arm shaft to operate the intake and exhaust valves when actuated by the camshaft. The rocker arms normally can slide (i.e., are axially moveable) on the rocker arm shaft. Stoppers are mounted on the rocker arm shaft to stop the axial movement of the rocker arms in one direction. Typically, coil springs also are mounted on the rocker arm shaft opposite to the stoppers, respectively, to urge the rocker arms toward the stoppers.
In some arrangements, the spring constant of each spring can be set at a relatively large value to retain the rocker arm in a precise position even when subject to large engine vibrations and shock. However, if the spring constant is excessively large, friction increases between the rocker arm and the spring, between rocker arms disposed next to each other, and between the rocker arm and the stopper. The friction causes wear of those members and more engine power is necessary to drive the camshaft in order to actuate the rocker arms.
If, on the other hand, the spring constant is excessively small, large shocks on and vibrations in the engine tend to displace the rocker arms from their precise positions. In addition, the spring occasionally can be jolted out of the its primary position or can be damaged by the shock. The shock can be particularly large in connection with an engine employed for an outboard motor. This is because the outboard motor is typically mounted on an associated watercraft with a drive unit, which carries an engine, capable to popping up when the drive unit strikes an obstacle such as driftwood. The engine experiences large shock forces, not only when the drive unit strikes the obstacle, but also as drive unit momentarily pops up and then returns to its normal trim position.
A need therefore exists for an improved rocker arm arrangement for an engine that can retain at least one rocker arm in a precise preset position without significantly increasing friction on the rocker arm, and that can inhibit movement of the rocker arm from its preset position when the engine is subjected to a large shock force.
In accordance with one aspect of the present invention, an internal combustion engine comprises an engine body. A moveable member is moveable relative to the engine body. The engine body and the moveable member together define a combustion chamber. The engine body defines an intake passage communicating with the combustion chamber at an intake port thereof and an exhaust passage communicating with the combustion chamber at an exhaust port thereof An intake valve is arranged to move between an open position and a closed position relative to the intake port. An exhaust valve is arranged to move between an open position and a closed position relative to the exhaust port. A camshaft is journaled for rotation within the engine body. A rocker arm shaft is also disposed within the engine body. At least first and second rocker arms are pivotally mounted on the rocker arm shaft. The first rocker arm cooperates with the intake valve. The second rocker arm cooperates with the exhaust valve. The camshaft actuates the intake and exhaust valves through the first and second rocker arms, respectively. At least one of the rocker arms is (and preferably both are) axially moveable along an axis of the rocker arm shaft. A stopper, which is disposed on the rocker arm shaft, is arranged to stop the axial movement of the rocker arm in one direction. A biasing member is mounted on the rocker arm shaft opposite to the stopper to urge the rocker arm toward the stopper. A block member is arranged to limit the axial movement of the rocker arm in a direction working against the biasing member.
In accordance with another aspect of the present invention, an internal combustion engine comprises an engine body. A moveable member is moveable relative to the engine body. The engine body and the moveable member together define a combustion chamber. The engine body defines an intake passage communicating with the combustion chamber at an intake port thereof and an exhaust passage communicating with the combustion chamber at an exhaust port thereof. An intake valve is arranged to move between an open position and a closed position relative to the intake port. An exhaust valve is arranged to move between an open position and a closed position relative to the exhaust port. A camshaft is journaled for rotation within the engine body. A rocker arm shaft is also disposed within the engine body. At least one intake rocker arm and at least one exhaust rocker arm are pivotally mounted on the rocker arm shaft. The camshaft actuates the intake and exhaust valves through the intake and exhaust rocker arms, respectively. At least one of the rocker arms is axially moveable along an axis of the rocker arm shaft. A stopper is disposed on the rocker arm shaft to stop the axial movement of the rocker arms in one direction. A biasing member is mounted on the rocker arm shaft opposite to the stopper to urge at least one of the rocker arms toward the stopper and to dampen the axial movement of the rocker arm in an opposite direction to the one direction. A protector is configured to protect the biasing member against shock caused by the axial movement of the rocker arm in the opposite direction.
In accordance with a further aspect of the present invention, an internal combustion engine comprises an engine body. A moveable member is moveable relative to the engine body. The engine body and the moveable member together define a combustion chamber. The engine body defines an intake passage communicating with the combustion chamber at an intake port thereof and an exhaust passage communicating with the combustion chamber at an exhaust port thereof. An intake valve is arranged to move between an open position and a closed position relative to the intake port. An exhaust valve is arranged to move between an open position and a closed position relative to the exhaust port. A camshaft is journaled for rotation within the engine body. A rocker arm shaft is also disposed within the engine body. At least first and second rocker arms are pivotally mounted on the rocker arm shaft. The first rocker arm cooperates with the intake valve. The second rocker arm cooperates with the exhaust valve. The camshaft actuates the intake and exhaust valves through the first and second rocker arms, respectively. The rocker arms are axially moveable along an axis of the rocker arm shaft. A stopper is disposed on the rocker arm shaft to stop the axial movement of the rocker arms in one direction. A spring member is disposed opposite to the stopper with at least one of the rocker arms disposed between the spring member and the stopper. The spring member includes a mounting section at which the spring unit is mounted onto the rocker arm shaft. The spring member further includes at least one leaf spring section that extends from the mounting section in another direction to acts against one of the first and second rocker arms that is disposed next to the spring member.
In accordance with a still further aspect of the present invention, an internal combustion engine comprises an engine body. A moveable member is moveable relative to the engine body. The engine body and the moveable member together define a combustion chamber. The engine body defines a passage communicating with the combustion chamber at a port thereof. A valve is arranged to move between an open position and a closed position relative to the port. A camshaft is journaled for rotation within the engine body. A rocker arm shaft is also disposed within the engine body. A rocker arm is pivotally mounted on the rocker arm shaft. The camshaft actuates the valve through the rocker arm. The rocker arm is axially moveable along an axis of the rocker arm shaft. A stopper is disposed on the rocker arm shaft to stop the axial movement of the rocker arm in one direction. Means are provided for biasing the rocker arm toward the stopper. Further means are provided for limiting the rocker arm from moving toward the means for biasing the rocker arm beyond a preset distance.